Magnetic structure and electronic properties of mixed-metal Ruddlesden-Popper oxide LaSrCo1/2Fe1/2O₄

Atomic, electronic, and magnetic structure of LaSrCo1/2Fe1/2O₄ mixed-metal Ruddlesden-Popper oxide is investigated theoretically using self-consistent ACBN0 DFT + U approach. We show that the electronic and magnetic properties strongly depend on the distribution of transition-metal and La/Sr ions in the lattice. Fe-Fe exchange is found to be antiferromagnetic, whereas Co-Co and Fe-Co exchange is ferromagnetic. We find that Co spin states depend on the distribution in both La/Sr and transition-metal ions. The most energetically favorable configuration is ferromagnetic, whereas the majority of metastable configurations are antiferromagnetic. LaSrCo1/2Fe1/2O₄ was synthesized using spray-pyrolysis method. Magnetization measurements revealed antiferromgnetic behavior, thus indicating presence of metastable configurations in the synthesized material. In addition, we show that in complex systems, such as mixed-metal Ruddlesden-Popper phases, Hubbard U values have to be determined for each crystallographically non-equivalent site.